Taking calcium and vitamin D supplements together may increase the risk of stroke, according to an analysis of trial data covering nearly one million participants.

US researchers set out to look at the role of nutritional supplements and different diets in preventing poor cardiovascular outcomes, but even the lead investigator cautions the evidence is not robust.

The team, led by Dr Safi Khan from the West Virginia University School of Medicine, identified only two of 16 nutritional supplements and one of eight dietary interventions that might be protective after examining data from 277 trials.

Their meta-analysis indicated, with moderate certainty, that a combination of calcium and vitamin D supplementation was associated with a 17% increased risk for stroke.